Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual clube recebeu um jogador DF gratuitamente?
 ###Tabelas: CREATE TABLE 2004_fixtures_and_results (2004_fixtures_and_results_id AUTO_INCREMENT PRIMARY KEY, Date VARCHAR, Competition VARCHAR, Venue VARCHAR, Result VARCHAR, Score VARCHAR, Goals VARCHAR) CREATE TABLE round_of_sixteen (round_of_sixteen_id AUTO_INCREMENT PRIMARY KEY, Team 1 VARCHAR, Agg. VARCHAR, Team 2 VARCHAR, 1st leg VARCHAR, 2nd leg VARCHAR) CREATE TABLE first_team (first_team_id AUTO_INCREMENT PRIMARY KEY, Exit Date VARCHAR, Pos. VARCHAR, Player VARCHAR, To club VARCHAR, Transfer fee VARCHAR) CREATE TABLE current_and_former_player_information (current_and_former_player_information_id AUTO_INCREMENT PRIMARY KEY, Name VARCHAR, Total W-L VARCHAR, Singles W-L VARCHAR, Doubles W-L VARCHAR, No. of ties INT, First year played INT, No. of years played INT) CREATE TABLE production_and_source (production_and_source_id AUTO_INCREMENT PRIMARY KEY, Country VARCHAR, Electricity production (Kw/h, billion) INT, % Coal INT, % Natural gas INT, % Oil INT, % Hydropower INT, % Other renewable INT, % Nuclear power INT)  
SELECT To club FROM first_team WHERE Transfer fee = free AND Pos. = df